US7119870B1 - Liquid crystal display device having particular drain lines and orientation control window - Google Patents

Abstract

When the orientation of liquid crystal molecules in a pixel are divided by an orientation divider, a boundary of the orientation is produced at any part of the pixel. A drain signal line (54) is formed to overlap with the boundary so that a light-shielding region in the pixel is decreased and an aperture ratio can be improved. Leakage of light caused when the orientation is disturbed can be shielded by the drain signal line (54), and contrast can be enhanced. The orientation divider can be an orientation control window (36), an orientation control slope (90) or the like.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device provided with an orientation divider for dividing the orientation direction of a liquid crystal.

2. Description of the Related Art

FIG. 1 shows a plan diagram of a conventional liquid crystal display device.FIG. 2 shows a sectional diagram taken along line B—B of FIG.1 andFIG. 3 shows a sectional diagram taken along line D—D of FIG.1.

In can be seen in FIG.2 andFIG. 3 that a plurality ofdrain signal lines50 and a plurality ofgate signal lines51 intersect each other on afirst substrate10 which is made of an insulating substrate such as glass or quartz, and in the vicinity of each intersection oflines50 and51 there are provided a thin-film transistor (hereinafter called TFT).Pixel electrodes19 made of a transparent conductive film such as ITO (Indium Tin Oxide) are connected tosources13s of the TFT. Thedrain signal lines50 are intersected with thegate signal lines51 and are overlapped with thepixel electrodes19.

A storagecapacitor electrode line52 is disposed near the TFT in parallel to thegate signal line51. The storagecapacitor electrode line52 is made of chromium and makes a storage capacitor for storing electric charges by forming a capacitor with anelectrode53 connected to thesource13s of the TFT through aninterlayer insulating film15. This storage capacitor is disposed to be electrically parallel to aliquid crystal21 which is also a capacitor in order to suppress the electric charges stored in theliquid crystal21 by a leak current of the TFT and to keep the stored electric charges.

Anopposing electrode34 on the side of asecond substrate30 is a common electrode which is formed to overlap the plurality ofpixel electrodes19. Anorientation control window36, which is formed by removing the ITO as an opposing electrode material so that one end of letter Y indicated by a dotted line inFIG. 1 is made to have the same forked shape as the other end, is disposed at positions corresponding to therespective pixel electrodes19.

As can be seen in FIG.2 andFIG. 3, theinterlayer insulating film15, thedrain signal line50 disposed for each pixel, and aplanarization insulating film17 are sequentially formed on theinsulating substrate10, while thepixel electrode19 made of ITO is disposed for each pixel on theplanarization insulating film17. Thepixel electrode19 is disposed to overlap with thedrain signal line50. Avertical orientation film20 for orienting theliquid crystal21 is further disposed on thepixel electrode19. Apolarizer41 is disposed on the opposite side of theinsulating substrate10 facing theliquid crystal21.

Acolor filter31 comprising red (R), green (G), and blue (B) for showing such colors and a black matrix for shielding light is disposed on the opposite side of thesecond substrate30 facing theliquid crystal21. Aprotective film33 made of a resin is formed on thecolor filter31 to protect its surface and theopposing electrode34, which is made of a transparent conductive film of ITO or the like, is formed on theprotective film33. As described above, theorientation control windows36 for controlling the orientation of theliquid crystal21 are formed on theopposing electrode34. Avertical orientation film35 which vertically orients theliquid crystal21 is disposed on theorientation control windows36. Apolarizer42 is disposed on the opposite side of thesecond substrate30 facing theliquid crystal21. Thepolarizer42 and thepolarizer41 are disposed so that their polarization axes intersect at right angles.

Theinsulating substrate10 and thesecond substrate20 are joined at their peripheries using a sealing adhesive agent (not shown), and a nematicliquid crystal21 which has a negative anisotropy of dielectric constant is filled in a gap formed to complete a liquid crystal display panel. Theorientation control windows36 formed in theopposing electrode34 are disposed at two positions for each pixel because theorientation control window36 shows the forked shape in letter Y in FIG.3.

Theliquid crystal21 has a negative anisotropy of dielectric constant. Here, the behavior of liquid crystal molecules will be described. In a state that a voltage is not applied to theliquid crystal21, the liquid crystal molecules between thesubstrates10 and30 are vertically oriented with respect to thesubstrates10,30. Therefore, incident light which is linearly polarized by thepolarizer41 on the side of theTFT substrate10 is not double refracted in theliquid crystal21 but shielded by thepolarizer42 on the side of thesecond substrate30 to show black. This is called a normally black method.

As shown inFIG. 2, when a voltage is applied to theliquid crystal21, the major axes of the liquid crystal molecules are oriented in the vertical direction with respect to the electric flux line, but controlled to incline in a plurality of orientation directions with respect to onepixel electrode19 by the electric flux line produced in a slanting direction at the end of thepixel electrode19 and the end of theorientation control window36. The incident light which is linearly polarized by thepolarizer41 becomes an elliptical polarized light upon receiving the double refractory by theliquid crystal21 which has a negative anisotropy of dielectric constant so to pass through thepolarizer42 and have a transmissivity corresponding to a voltage of the drain signal line.

Thus, when the orientation direction of the liquid crystal is divided into multiple numbers in the pixel, the respective regions have a different viewing angle characteristic so that the viewing angle of the pixels as a whole can be enlarged.

In this specification, a means for dividing the orientation direction of the liquid crystal (orientation divider) is indicated as an orientation divider. In addition to the orientation divider described above, other arts, such as an orientation control slope or division of a rubbing direction into multiple numbers, have been proposed.

In the state that a voltage is applied to theliquid crystal21, however, the liquid crystal molecules as a continuous body are continuously inclined to allow the passage of light according to an electric field produced at the edge of theorientation control window36 outside the region of theorientation control window36 formed on theopposing electrode34, but, in the region of theorientation control window36, the liquid crystal molecules remain in the vertically oriented state with respect to thesubstrates10,30, so that the light does not pass through the orientation control window and a light-shielding state is kept.

Even when an orientation divider other than the orientation control window is used, a boundary in the orientation direction of the liquid crystal may exist at any position. Such a boundary in the orientation direction is consistently in a state of shielding the light in a normally black mode type and in a state of allowing the light in a normally white mode type because the orientation does not change even if a voltage is applied to between the electrodes.

As shown in FIG.1 throughFIG. 3, thedrain signal lines50 overlap with thepixel electrodes19 and made of a light-shielding material such as metal. However, when thedrain signal line50 is disposed between thepixel electrodes19, the liquid crystal is oriented by a signal voltage applied to thedrain signal line50, which results in degraded display quality.

Therefore, there are disadvantages in the conventional art that an effective display region in the pixel electrode forming region must decreased because of theorientation control windows36 and thedrain signal lines50, an aperture ratio was heavily degraded, and a bright display could not be obtained.

SUMMARY OF THE INVENTION

The present invention was conceived in response to the disadvantages described above. It is an object of the present invention to provide a liquid crystal display device which has a wide viewing angle and can provide bright display with an improved aperture ratio.

The invention was created to remedy the disadvantages as described above. The invention is a liquid crystal display device which controls the orientation of a liquid crystal by means of a plurality of pixel electrodes formed for each pixel and an opposing electrode formed to cover the plurality of pixel electrodes, which has an orientation divider for dividing an orientation direction of the liquid crystal into a plurality of orientation directions within a single pixel and a light-shielding film formed to overlap with boundaries of the orientation directions of the liquid crystal formed by the orientation divider.

According to another aspect of the invention, the liquid crystal of the liquid crystal display device is sealed between a first substrate and a second substrate which are disposed so as to oppose each other; the first substrate has gate signal lines, drain signal lines, and switching elements connected to the gate signal lines and the drain signal lines; the pixel electrodes are connected to the switching elements; and the opposing electrode is formed on the second substrate to oppose the liquid crystal.

Thus, the present invention has an orientation divider for dividing the orientation direction of the liquid crystal into a plurality of directions in a single pixel, and a light-shielding film is disposed to overlap with the boundaries of the orientation directions produced by the orientation divider. The boundaries of the orientation directions of the liquid crystal exhibit a light-shielding function under a normal situation, so that an area of the light-shielding region for each pixel does not change, even when the light-shielding film overlaps the boundaries. As compared with a liquid crystal display device which has the light-shielding film formed not to overlap with the boundaries of the orientation, the area of the light-shielding region can be decreased, and an aperture ratio of the liquid crystal display device can be improved.

In a plan view, the light-shielding film overlaps the boundaries of the orientation directions of the liquid crystal, so that light can be prevented from leaking out of the liquid crystal display device by virtue of the presence of the light-shielding film. Even if the orientation of the liquid crystal is disturbed in the vicinity of the boundary in the orientation direction of the liquid crystal to weaken a light-shielding property at the boundary, higher contrast images can still be displayed.

According to another aspect of the invention, the orientation divider divides the orientation directions of the liquid crystal by generating an electric field which is inclined with respect to the normal line of the pixel electrode and/or the opposing electrode.

In the liquid crystal display device which divides the orientation directions of the liquid crystal by forming the electric field which is inclined with respect to the normal line of the pixel electrode and/or the opposing electrode, orientation direction restraint ability of the orientation divider is weak compared with when the orientation is controlled by rubbing or the like, so that the orientation of the liquid crystal tends to be disturbed, and light may leak in the vicinity of the boundary in the orientation direction. The present invention, however, can securely shield the light in the vicinity of the boundary in the orientation direction because the light-shielding film is disposed to overlap with the boundary.

According to another aspect of the present invention, the light-shielding film is a conductive substance made of metal, e.g., the drain signal line. When a storage capacitor electrode for forming the storage capacitor on each pixel electrically connected in parallel with the liquid crystal is provided, the storage capacitor electrode can also be used as the light-shielding film.

According to still another aspect of the present invention, the liquid crystal has a negative anisotropy of dielectric constant, and a vertical orientation film is formed to cover the pixel electrodes.

Thus, by using as the light-shielding film the storage capacitor electrode when the conductive substance is made of metal, e.g., the drain signal line or the storage capacitor electrode, is provided, an aperture ratio is not substantially lowered, even when the drain signal line or the storage capacitor electrode is disposed in the pixel region.

Where the drain signal line is disposed between the pixels, the electric field produced by the drain signal line leaks to a layer of the liquid crystal and the orientation direction of the liquid crystal may be disturbed because the drain signal line is not shielded by the pixel electrode. However, where the drain signal line is arranged to overlap with the boundary in the orientation direction, the aperture ratio is not lowered even if the drain signal line is present in the pixel region. Therefore, the drain signal line can be disposed on a layer below the pixel electrode. Then, the electric field of the drain signal line can be shielded by the pixel electrode, and the orientation of the liquid crystal can be prevented from being disturbed.

According to still another aspect of the present invention, the orientation divider is an orientation control window, which is formed at a position to overlap with the pixel electrode of the opposing electrode, or an orientation control slope.

According to a still further aspect of the present invention, the orientation control slope is formed by having a projection made of an insulating substance formed on the pixel electrode and/or the opposing electrode.

The orientation control slope may be formed by having a projection made of an insulating substance formed between the pixel electrode and the first substrate and/or between the opposing electrode and the second substrate.

According to yet another aspect of the invention, a liquid crystal display device is characterized in that liquid crystal is sealed between a first substrate and a second substrate which are disposed so as to oppose each other; the first substrate has switching elements connected to gate signal lines and drain signal lines, pixel electrodes which are connected to the switching elements and made of a conductive material and a vertical orientation film for orienting the liquid crystal; the second substrate has an opposing electrode which has the orientation control window (formed as an orientation divider) at positions that overlap with the pixel electrodes to control the orientation of the liquid crystal and a vertical orientation film for orienting the liquid crystal; and the drain signal lines are disposed on the first substrate at positions that overlap with the orientation control windows.

According to yet another aspect of the invention, a liquid crystal display device is characterized in that liquid crystal is sealed between a first substrate and a second substrate which are disposed so as to oppose each other; the first substrate has gate signal lines, drain signal lines, switching elements connected to the gate signal lines and the drain signal lines, pixel electrodes connected to the switching elements and made of a conductive material, storage capacitor signal lines for forming the storage capacitors with semiconductor layers of the switching elements, and a vertical orientation film for orienting the liquid crystal; the second substrate has an opposing electrode which controls the orientation of the liquid crystal and has the orientation control windows (formed as an orientation divider) at positions that overlap with the pixel electrodes and a vertical orientation film for orienting the liquid crystal; and a part of the gate signal lines, a part of the storage capacitor signal lines and the drain signal lines are disposed on the first substrate at positions that overlap with the orientation control windows.

According to another aspect of the invention, the orientation divider such as the orientation control window has a width different from that of the light-shielding film or the signal line overlapping the orientation control window or the like.

Because the width of the orientation control window is thus different from the width of the signal line overlapping it, specifically the drain signal line, and when a part of the gate signal line and the storage capacitor signal line also overlaps the orientation control window, the width of a part of the gate and the storage capacitor signal line, the orientation can be prevented from being disturbed and the light from leaking, even if the orientation control window and the drain signal line or the like are not correctly aligned.

According to a still further aspect of the present invention, the pixel electrodes are disposed in a matrix; the drain signal lines are connected to a plurality of pixel electrodes in the same column via the switching elements; the pixel electrodes which are connected to the same drain signal line and positioned in the mutually adjacent rows are disposed to displace by a distance corresponding to about 1.5 pixels or smaller in a direction that the gate signal lines are extended.

For example, the pixel electrodes positioned on the adjacent rows are displaced by about 1.2 pixels from each other, and the pixel electrodes connected to the same drain signal line have a corresponding color filter with the same color.

Where the pixel electrodes (the electrodes designed to indicate the same color) positioned on the adjacent rows are in a so-called delta arrangement in which they are displaced by about 1.5 pixels in the direction that the gate signal lines are extended, the drain signal lines are disposed in a meandering or zigzag pattern so that the drain signal lines overlap the boundaries in the orientation directions of the liquid crystal of the respective displaced pixels. Thus, an aperture ratio is prevented from lowering, light can be prevented from leaking from the respective pixels, and the display quality of the device can be improved. Also, where the displacement of the pixels between the neighboring rows is smaller than 1.5 pixels (e.g., 1.2 pixels), the drain signal line extends while bending to pass through the pixel regions of the same color in the same way as the delta arrangement but its length is shorter than that in the delta arrangement. Therefore, the drain signal line can have a lower resistance than in the delta arrangement.

In another aspect, the present invention is in the form of a liquid crystal display device for displaying by controlling the orientation of a liquid crystal of each pixel by means of a plurality of pixel electrodes formed for respective pixels and an opposing electrode disposed to oppose the plurality of pixel electrodes with the liquid crystal therebetween, which comprises an orientation divider for forming a boundary in the orientation direction of the liquid crystal in a single pixel; wherein a light-shielding film is disposed so that at least a part of it is arranged through the pixel electrode region so to overlap with the boundary in the orientation direction of the liquid crystal.

According to another aspect of the present invention, the light-shielding film is a drain signal line for supplying the switching element disposed for each pixel with a display signal in order to control the orientation of the liquid crystal for each pixel.

Thus, even when the drain signal line passes through the pixel electrode regions, the aperture ratio is not lowered because the drain signal line inherently passes along the boundary in the orientation direction of the liquid crystal.

According to still another aspect of the present invention, in the aforesaid liquid crystal display device, a plurality of pixels are disposed as a matrix and corresponded with any of red, green, and blue colors to be displayed; the pixels having the same color are displaced from each other in a direction of the row between the adjacent rows; and the drain signal line is extended in a direction of the column in a zigzag form so to overlap with at least a part of the boundary in the orientation direction of the liquid crystal formed in the pixel electrode region of the pixels with the same color displaced in the respective rows and supplies the pixels of the same color with a display signal through the switching element.

And, according to a still further aspect of the invention, in the aforesaid liquid crystal display device, the drain signal line is bent to extend in a direction of the column so to cross the one and same pixel electrode region a plurality of times.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan diagram of a conventional liquid crystal display device;

FIG. 2 is a sectional diagram of the liquid crystal display device taken along line B—B ofFIG. 1;

FIG. 3 is a sectional diagram of the liquid crystal display device taken along line D—D ofFIG. 1;

FIG. 4 is a plan diagram of a liquid crystal display device according to a first embodiment of the invention;

FIG. 5 is a sectional diagram of the liquid crystal display device taken along line A—A ofFIG. 4;

FIG. 6 is a sectional diagram of the liquid crystal display device taken along line B—B ofFIG. 4;

FIG. 7 is a plan diagram of a liquid crystal display device according to a second embodiment of the invention;

FIG. 8 is a sectional diagram of the liquid crystal display device taken along line C—C ofFIG. 7;

FIG. 9 is a plan diagram of a liquid crystal display device according to a third embodiment of the invention;

FIG. 10 is a sectional diagram of the liquid crystal display device taken along line D—D ofFIG. 9;

FIG. 11 is a plan diagram of a liquid crystal display device according to a fourth embodiment of the invention;

FIG. 12 is a plan diagram of a layout of pixels and drain signal lines of a liquid crystal display device according to a fifth embodiment of the invention;

FIG. 13 is a plan diagram of the liquid crystal display device according to the fifth embodiment of the invention;

FIG. 14 is a plan diagram of a liquid crystal display device according to a sixth embodiment of the invention;

FIG. 15 is a sectional diagram of the liquid crystal display device taken along line E—E ofFIG. 14;

FIG. 16 is a sectional diagram of a liquid crystal display device according to another embodiment of the invention; and

FIG. 17 is a sectional diagram of a liquid crystal display device according to another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment:

A liquid crystal display device of the present invention will be described.

FIG. 4 is a plan diagram of a liquid crystal display device of the invention,FIG. 5 is a sectional diagram of the liquid crystal display device taken along line A—A ofFIG. 4, andFIG. 6 is a sectional diagram of the liquid crystal display device taken along line B—B of FIG.4.

As shown inFIG. 4, a plurality ofgate signal lines55 each integrally having agate electrode11 are disposed horizontally, and a plurality ofdrain signal lines54 are disposed vertically. A thin-film transistor (TFT), which is a switching element, is disposed in the vicinity of each intersection of thegate signal line55 and thedrain signal line54, and apixel electrode19 made of a transparent conducting material such as ITO is connected to the TFT.

FIG. 4 shows thatorientation control windows36, which are formed by removing the ITO, which is a material for the opposing electrode in the same way as shown inFIG. 1, are disposed on the same side of an opposingelectrode34 facing asecond substrate30. Theorientation control window36 has a shape that the bottom end of letter Y indicated by a dotted line has the same forked shape as the top end, namely two letters Y are mutually connected with one of them turned upside down. In other words, theorientation control window36 has a shape that either end of its center region, which is rectangular and extending in a longitudinal direction of each pixel, is forked into two to extend toward two corners of the pixel.

The structure described above is substantially the same as that of a conventional liquid crystal described elsewhere in this specification. A feature of this embodiment is that thedrain signal line54 is formed along theorientation control window36 disposed on thesecond substrate30. InFIG. 4, thedrain signal line54 in the vicinity of the TFT enters the pixel region from its upper left, bends to extend in the lower right-hand direction to follow abranch section36aat the upper left part of theorientation control window36, and at asection36bof theorientation control window36 extending vertically inFIG. 4, extends vertically in the same way. Thedrain signal line54 further bends to extend in the lower left direction to follow abranch section36cextending in a lower left direction of theorientation control window36, leaves the pixel from its lower left, and extends to a pixel in the next row. Thus, thedrain signal line54 is disposed to overlap with the left-side branch sections and the vertical section of theorientation control window36.

The liquid crystal immediately below theorientation control window36 keeps a vertically oriented state because an electric field is not produced and the orientation is not controlled. Therefore, it becomes a light-shielding region which always does not allow the passage of light. In this embodiment, thedrain signal line54 which is a metal line and has a light-shielding function is disposed there, so that the two light-shielding regions are overlapped. As a result, the light-shielding region occupying the pixel region becomes small, and an aperture ratio is improved. The region immediately below theorientation control window36 is a boundary of the liquid crystal in its orientation direction in the pixel, so that the orientation direction tends to be disturbed. When the orientation direction is disturbed, light may leak erroneously. But, since thedrain signal line54 having the light-shielding function is disposed in this embodiment, the present invention can prevent the light from leaking and can further enhance contrast.

It is here desirable that a width54wof thedrain signal line54 be different from a width36wof theorientation control window36. If they have the same size, thedrain signal line54 and theorientation control window36 are displaced from each other when both thesubstrates10,30 are bonded but not correctly aligned. Therefore, the region for shielding the light is increased for the segment of the displacement, the aperture ratio is lowered, and the respective pixels are made to have variable aperture ratios. By having either of the widths made lager than the other in advance, the light-shielding region does not come to have a width larger than the predetermined width when the displacement is within a range of the difference in width even if the bonding is made with some displacement. Thus, variations among the respective pixels can be prevented. Either of the widths54wand36wmay be made larger, but if the width36wof theorientation control window36 is excessively narrow, the orientation direction cannot be divided securely, so that it is desirable to make the width36wof theorientation control window36 larger. However, when the width54wof thedrain signal line54 is made large, its electric resistance can be lowered, so that when the width36wof theorientation control window36 is sufficiently secured, the width54wof thedrain signal line54 can be made much larger. In this embodiment, theorientation control window36 is determined to have a width of 6 to 8 μm for example, then thedrain signal line54 is determined to have a width of 4 μm.

Next, a sectional structure of the liquid crystal display device taken along line A—A ofFIG. 4 will be described. As shown inFIG. 5, agate electrode11 made of refractory (high melting point) metal such as chromium (Cr) or molybdenum (Mo), agate insulating film12, and anactive layer13 made of a polysilicon film are formed in this order on an insulatingsubstrate10 made of quartz glass, non-alkali glass or the like.

In anactive layer13, achannel13cis disposed above thegate electrode11, and asource13sand adrain13d, which are formed by ion doping with astopper insulating film14 on thechannel13cused as a mask, are disposed on either side of thechannel13c.

An interlayer insulatingfilm15 comprising Sio₂film, SiN film, and then SiO₂film laminated in this order is formed to fully cover thegate insulating film12, theactive layer13, and thestopper insulating film14, and metal such as A1 is filled into a contact hole formed to correspond to thedrain13dto form adrain electrode16. Further, aplanarization insulating film17 which is made of, for example, an organic resin is formed to fully cover theinterlayer insulating film15 to provide a flat surface. A contact hole is formed in theplanarization insulating film17 at a position corresponding to thesource13s, and apixel electrode19 which is made of a transparent conductive material such as ITO and in contact with thesource13sthrough the contact hole is formed on theplanarization insulating film17. Avertical orientation film20, which is made of an organic resin such as a polyimide and vertically orients aliquid crystal21 having a negative anisotropy of dielectric constant, is formed on thepixel electrode19. Rubbing treatment of thevertical orientation film20 is not required. Apolarizer41 is disposed on the outside of the insulatingsubstrate10, namely on the side not facing to the liquid crystal.

Acolor filter31 comprising respective colors R, G, and B, and ablack matrix32 having a light-shielding function and aprotective film33 made of an acrylic resin or the like for protecting thecolor filter31 are disposed inside of thesecond substrate30, specifically on the side facing theliquid crystal21 of thesecond substrate30. The opposingelectrode34 which is opposed to therespective pixel electrodes19 and partly provided with theorientation control window36 is disposed on theprotective film33. Avertical orientation film35 made of a polyimide is formed on the entire surface of the opposingelectrode34.

Apolarizer42 is disposed on the opposite side of thesecond substrate30 facing theliquid crystal21, being the side where aviewer101 will view the display.

In addition, theliquid crystal21 used is one having a negative anisotropy of dielectric constant. Specifically, the liquid crystal shall have the liquid crystal molecules vertically oriented with respect to the substrate when a voltage is not applied and oriented substantially in parallel when a voltage is applied.

The insulatingsubstrate10 having the TFT produced as described above and the opposingsubstrate30 provided with theorientation film35 and the opposingelectrode34 facing thesubstrate10 are mutually adhered by applying a sealing adhesive agent (not shown) to their peripheries.Liquid crystal21 is filled into the space formed between them to complete the liquid crystal display panel.

By disposing thedrain signal line54 at the position corresponding to theorientation control window36 as described above, the boundary in the orientation direction can be overlapped with the region keeping to shield light, which is called wiring. In other words, a portion of light shielding effected by a conventional drain signal line can be removed, and the aperture ratio can be improved. Because the width of thedrain signal line54 differs from that of theorientation control window36, the light-shielding section does not have a width exceeding the predetermined level, and the aperture ratios of respective pixels do not vary.

Second Embodiment:

FIG. 7 is a plan diagram of a liquid crystal display device according to a second embodiment of the present invention, andFIG. 8 is a sectional diagram of the liquid crystal display device taken along line C—C of FIG.7. This embodiment corresponds to that of the first embodiment in that thedrain signal lines54 are disposed at the positions corresponding to theorientation control windows36 formed on the opposingelectrode34, but differs in thatportions36d,36eof theorientation control window36, which are not covered with thedrain signal line54, overlapregions37,38 branched from astorage capacitor electrode53 and thegate signal line55 to fully cover theorientation control window36.

The structure of the liquid crystal display device of this embodiment will be described with reference to FIG.7 and FIG.8. Thegate signal lines55 which havegate electrodes11 partly made of refractory (high melting point) metal such as Cr or Mo, and storagecapacitor electrode lines52 are simultaneously formed on the insulatingsubstrate10 made of quartz glass, non-alkali glass or the like as shown in the drawings. At this point, thegate signal lines55 and the storagecapacitor electrode lines52 correspond to theorientation control windows36 by theirportions37,38 to cover the sections which are not covered with thedrain signal line54. Specifically, as shown inFIG. 7, theorientation control window36eon the side close to thegate signal line55 has a part of thegate signal line55 indirectly overlapping theoverlap electrode38 having a shape corresponding to theorientation control window36, and anorientation control window36don the side close to the other storagecapacitor electrode line52 has a part of thestorage capacitor electrode53 indirectly overlapping theoverlap electrode37 having a shape corresponding to theorientation control window36.

Thus, the aperture ratio can be improved by having thedrain signal lines54 overlapped with theorientation control windows36 which are always in the light-shielding state in the same way as in the first embodiment.

The division of the orientation division in this embodiment is controlled according to the direction of the electric field only, so that restraint ability of the orientation direction of the liquid crystal is low as compared with, for example, the rubbing treatment. Therefore, the orientation may be disturbed by an external factor such as an external magnetic field. On the other hand, in this embodiment, even a region which does not overlap with thedrain signal line54 of theorientation control window36 is arranged to overlap with theoverlap electrodes37,38, so that the shielding of light by theorientation control window36 of the pixel can be made perfect. Therefore, even if light leaks in case of the disturbance of the orientation of the liquid crystal of theorientation control window36, it can be shielded completely, and complete black display can be made when black color is displayed. Thus, high-contrast display can be made.

Since thestorage capacitor electrode53 made of the same polysilicon film as theactive layer13 is disposed to overlap with theoverlap electrode37 branched from the storagecapacitor electrode line52, the storage capacitor is increased. Further, because thestorage capacitor electrode53 overlaps theorientation control window36, the aperture ratio is not lowered by the increase in area of the storage capacitor.

It is desirable that either thedrain signal line54 or theorientation control window36 have a width larger than the other in the same way as in the first embodiment. Similarly, theoverlap electrodes37,38 and theorientation control windows36d,36epreferably have a different width so that either pair of them has a larger width than the other pair.

As shown inFIG. 7, a single pixel is divided into fourregions19U,19D,19R and19L by theorientation control window36 and thedrain signal line54. Among them, it is preferable that thepixel region19L on the left side of thedrain signal line54 has the same area as thepixel region19R on its right side.

At an end of thepixel electrode19, the liquid crystal molecules are stabilized by having an angle of inclination from the direction of the normal line depending on the intensity of the electric field controlled and the direction of inclination controlled by the electric field produced obliquely to expand toward the opposingelectrode34.

The directions of inclination of the liquid crystal molecules at the ends of thepixel electrode19 are different among the four regions divided by theorientation control window36.

The liquid crystal molecules having their orientation controlled in different directions in the respective regions of thepixel electrode19 are influenced toward the center of the pixel electrode because of the continuity of the liquid crystal. Specifically, the orientation direction of the liquid crystal molecules in the vicinity of the center is controlled so as not to be substantially oblique with respect to the direction of the normal line of the panel due to the presence of theorientation control window36 disposed on the opposingelectrode34 and less influenced by the orientation control by theorientation control window36 as the liquid crystal molecules are away from the vicinity of the center. The liquid crystal molecules are oriented to be parallel to the substrate because of the potential difference between thepixel electrode19 and the opposingelectrode34.

Therefore, the orientation direction of the liquid crystal in thepixel region19L is oblique from the side of the insulatingsubstrate10 in the direction of an arrow19La inFIG. 7, and the orientation direction of the liquid crystal in thepixel region19R is oblique in the direction of an arrow19Rb in FIG.7. Accordingly, when the liquid crystal display panel is seen from the right or left direction, a viewing angle from either direction becomes large, so that a wide viewing angle can be realized. When the right and leftpixel regions19R,19L have a different area, a viewing angle from, for example, the right side, becomes large, but a viewing angle from the left side becomes narrow. Therefore, the right and leftpixel regions19R,19L are made to have the same area.

The liquid crystal molecules of the upper andlower pixel regions19D,19U are obliquely oriented from the side of the insulatingsubstrate10 toward the directions of arrows19Dc,19Ud. In order to have the same viewing angle from the right and left directions and also to have the same viewing angle when viewed from the upper and lower directions, it is desirable to form thepixel regions19D,19U with the same area.

Third Embodiment:

FIG. 9 is a plan diagram of the third embodiment, andFIG. 10 is a sectional diagram taken along line D—D of FIG.9. The subject matter of this embodiment is the same as the second embodiment. In the second embodiment, theoverlap electrodes37,38 were formed by partly branching thegate signal line55 and thestorage capacitor electrode53. This embodiment differs from that of the second embodiment in that a light-shieldingfilm56 is made of a light-shielding material such as metal which is different from thegate signal line55 and thestorage capacitor electrode53. Thus, the same effect as in the second embodiment can be obtained by using a different body to form the light-shieldingfilm56.

In this embodiment, the light-shieldingfilm56 is described as being disposed on a layer different from the drain signal line, but the present invention is not limited to such a configuration. The light-shielding layer may be formed on the same layer as the drain signal line at the same time when the drain signal line is formed and may be formed with the drain signal line in one body, or the light-shielding film may be formed on the side of thesecond substrate30, for example, on the same layer as theblack matrix32.

Fourth Embodiment:

FIG. 11 shows a plan diagram of the fourth embodiment. This embodiment adopts a delta arrangement in that thepixel electrodes19 are connected to the samedrain signal line60, and therespective pixel electrodes19 in the adjacent row are displaced by 1.5 pixels in the extending direction of agate signal line51. The delta, arrangement is extensively used in an audiovisual field for DSC (digital still camera) and the like used to show video.

In the delta arrangement, when attention is directed to one specific row, respective colors of a pixel (R) for red color, a pixel (G) for green color and a pixel (B) for blue color are repeatedly arranged in this order, and in the next row, the same respective colors as those in the first row are repeatedly arranged in the same way except that the arranged positions of the respective colors are displaced to the right by 1.5 pixels with respect to the first row.

As shown inFIG. 11, a TFT is formed in the vicinity of the intersection between thegate signal line55 which is linearly arranged from side to side and thedrain signal line60 which is connected to the same color pixels. This TFT has thegate electrode11 which forms a part of thegate signal line55 and thesemiconductor layer13 made of polysilicon which comprises thedrain13dconnected to thedrain signal line60 and thesource13sconnected to thepixel electrode19. Thedrain signal line60 is connected to the same color pixels which are displaced by the segment of 1.5 pixels in the direction of the column. Accordingly, thedrain signal line60 arranged so as to overlap theorientation control window36 of each pixel is bent from a corner of thepixel electrode19 toward the vicinity of the center and, as a whole, extends in a zigzag form so to cross the respective center regions of the same color pixels displaced by 1.5 pixels. In the same way as in the previous embodiments, theorientation control window36 has a shape-that one of two conjoined letters ‘Y’ with portions extending toward the corners of the pixel electrode and in the vertical direction (the portion extending along the sides of the pixels). Thedrain signal line60 extended from the upper left of the pixel extends in a lower right direction along theregion36aat the upper left of theorientation control window36, in a vertical direction along theregion36band in a lower left direction along theregion36cand leaves the pixel from the lower left of the pixel electrode. Subsequently, thedrain signal line60 enters the next pixel which is displaced to the left by 1.5 pixels from its upper right section, extends in a lower left direction along theregion36dat the upper right section of theorientation control window36, in a vertical direction along theregion36band in a lower right direction along the lowerright region36eand leaves the pixel. The same pattern is repeated so that thedrain signal line60 is disposed to extend in a zigzag pattern in the direction of the column.

At the intersection of the storagecapacitor signal line52 and adrain signal line50, a short-circuit prevention film57 is intervened in a shape corresponding to the intersection between them to prevent the signal lines52,50 from short circuiting. The short-circuit prevention film57 can be formed of a semiconductor film, for example, a polysilicon film or the like which is used as the active layer of the TFT.

Thus, the short-circuit prevention film57 can be formed without adding a special process by applying the material which is used for the TFT to the short-circuit prevention film57. Since thedrain signal line60 is arranged as described above, thedrain signal line60 in the delta arrangement can be arranged in the shortest distance. Therefore, there is also provided an effect that any increase of wiring resistance caused by a longdrain signal line60 can be prevented.

Further, a separate light-shielding film may be formed at theorientation control window36 where light is not shielded in the same way as in the second and third embodiments.

Fifth Embodiment:

As described above, in the fourth embodiment thedrain signal line60 can be arranged along the shortest length according to the delta arrangement with the pixels displaced by 1.5 pixels, but thedrain signal line60 is still very long and has a large wiring resistance. Especially, a high-resolution liquid crystal display device requires that thedrain signal line60 be made thin, so that a video signal is rounded (delayed) due to the wiring resistance at a part away from the signal input section, and normal display may not be obtainable.

Where thedrain signal line60 is extended from asingle pixel72 to thenext pixel73 in order to connect the respective pixels arranged in the pattern displaced by 1.5 pixels, its oblique angle is gentle as compared with its extension to apixel74 positioned just below thepixel72. Specifically, thestorage capacitor electrode53 which forms the capacitor with the storagecapacitor signal line52 has a small intersection angle with respect to the storagecapacitor signal line52, so that the area of the overlapped section also becomes small. Thus, despite the ratio of sacrificing the aperture ratio, a large, storage capacitor cannot be obtained, and efficiency is not high. As a result, should TFT current leak, voltage applied to the liquid crystal may not be retained.

The fifth embodiment, then, efficiently forms a large storage capacitor which is sufficient to retain the orientation of the liquid crystal for a predetermined period even if TFT had a leak current.FIG. 12 is a plan diagram showing a positional relation of pixels, drain signal lines and gate signal lines of the liquid crystal displace device of this embodiment.FIG. 13 is a partially expanded plan diagram showing the vicinity of some pixels of the liquid crystal display device.

As shown in FIG.12 andFIG. 13, thepixels19 of the liquid crystal display device are arranged in a matrix. In the first row at the top in the drawings, a pixel (R) showing red color, a pixel (G) showing green color and a pixel (B) showing blue color are repeatedly arranged in this order. In the next row below the first row, the same three color pixels are repeatedly arranged in the same way, except that the arranged positions of the respective colors are displaced to the right by 1.2 pixels with respect to the first row.

Therefore, thedrain signal line50 which is vertically extended to connect the pixels to supply the same drain signal can be made to have a much shorter wiring length than in the fourth embodiment. Accordingly, the wiring resistance can be lowered, and a uniform display can be created over the entire surface of the display area.

In this embodiment, since the vertically neighboringpixels19 which are connected to the samedrain signal line60 are displaced by only 1.2 pixels from each other between adjacent rows, thedrain signal line60 has a smaller bending angle. Since thecapacitor electrode53 is formed to oppose a region not overlapped with thedrain signal line60 of the storagecapacitor signal line52, a parallelogram surrounded by thedrain signal line60 and the storagecapacitor signal line52 is formed. Therefore, thedrain signal line60 has a small bending angle, the parallelogram of thecapacitor electrode53 has a small inclination at its both sides and comes to have a shape similar to rectangular. As the tops facing each other with the center therebetween are fixed depending on the pixel size, the pitch, and the width of the storagecapacitor signal line52, when the parallelogram of thecapacitor electrode53 has a large inclination at both sides, the area of the parallelogram grows small. Therefore, according to this embodiment capable of decreasing the bending angle of thedrain signal line60, thecapacitor electrode53 can have a large area, and the storagecapacitor signal line52 and thecapacitor electrode53 can have a large overlapped area. In this way, the storage capacitor is increased, and the voltage applied to the liquid crystal can be retained even if TFT has a leak voltage. The liquid crystal can be stably driven, and a quality display can be obtained.

Because thedrain signal line60 has a small bending angle, thedrain signal line60 has a much shorter wiring length as compared with the aforesaid embodiments. Therefore, the wiring resistance can be decreased, and more uniform display can be obtained on the entire surface of the display area.

Also, the overlap area of the storagecapacitor signal line52 and thecapacitor electrode53 can be made large, and driving stability of the liquid crystal can be further improved.

In the above description of a preferred embodiment, the pixels of the adjacent rows connected to the same drain signal line are displaced by 1.2 pixels in the row direction. However, the invention is not limited to such an arrangement. When the displacement is smaller than 1.5 pixels forming the delta arrangement, preferably in a range of one pixel or more and less than 1.5 pixels, high-resolution display can be obtained depending on the delta arrangement.

Sixth Embodiment:

In the aforesaid first to fifth embodiments, theorientation control window36 was used as the orientation divider. However, the orientation divider is not limited to theorientation control window36. This embodiment has an orientation control slope formed as the orientation divider.FIG. 14 is a plan diagram of the liquid crystal display device of this embodiment, andFIG. 15 is a sectional diagram of FIG.14.

In this embodiment, the orientation direction of the liquid crystal is divided by anorientation control slope90. Specifically, theorientation control slope90 is one example of the orientation divider. Since theorientation control slope90 is an insulating substance, an electric line of force produced between thepixel electrode19 and the opposingelectrode34 avoids theorientation control slope90 in an oblique direction as indicated by dotted lines in FIG.15. Thus, the orientation direction of the liquid crystal in the pixel is divided in the same way as theorientation control window36 of the first to fifth embodiments, and a viewing angle can be expanded. The orientation control slope is described in detail in Japanese Patent Application No. Hei 6-104044, and its description is not repeated here.

A firstorientation control slope90 is formed on the side of thefirst substrate10 to extend from the upper left of a pixel in a particular row to its lower right so to cross the pixel to leave the pixel temporarily at the middle right side of the pixel, to bend so to reenter the same pixel region, to cross it again in the lower left direction and to leave the pixel. A secondorientation control slope91 is formed on the side of thesecond substrate30 substantially in parallel to the firstorientation control slope90. Theorientation control slope90 and theorientation control slope91 formed on the side of the second substrate are alternately formed as shown in the plan diagram of FIG.14. The orientation control slopes90,91 are insulating and formed on thevertical orientation films20,35 respectively.

In those orientation control slopes, the major axes of the liquid crystal molecules just above the orientation control slopes remain es directed in the vertical direction so to form a region wherein light is shielded. Then, this embodiment formsdrain signal lines80 to overlap with the orientation control slopes90. With such an arrangement, the light-shielding region can be formed in the overlapped form in the same way as in the aforesaid embodiments, so that the aperture ratio can be improved. Further, theorientation control slope90 temporarily crosses the pixel and bends outside of the pixel electrode. Because the drain signal line is formed along theorientation control slope90, it also bends outside of the pixel electrodes. At the bent part of the drain signal line within the pixel, the electric field tends to concentrate but since the bent part is outside of the pixel electrode, the possibility of influencing on the orientation of the liquid crystal is lowered.

Theorientation control slope90 may be formed between thepixel electrode19 and thefirst substrate10 to form a slope on the surface of thepixel electrode19, as shown inFIG. 17 for example. In this case, an oblique electric field is produced because of the slope of the pixel electrode. Meanwhile, theorientation control slope90 may be formed between thepixel electrode19 and thevertical orientation film20. In this case, the orientation is divided by the slopedvertical orientation film20. In any event, since the region just above theorientation control slope90 keeps to shield light, the aperture ratio can be improved by disposing thedrain signal line80 there.

Theorientation control slope90 may have the same “conjoined Y” shape as in the first to fifth embodiments. However, theorientation control slope36 may also be formed in a shape such that the region extending to the upper right and the region extending to the lower right are connected, as in this embodiment for example.

Naturally, the orientation control window and the orientation control slope may be combined as the orientation divider. For example,orientation control windows93 are formed in thepixel electrode19 and the orientation control slopes91 are formed on the opposingelectrode34 as shown in the sectional diagram of FIG.16.FIG. 16 is a sectional diagram showing a single pixel in which thepixel electrode19 is shown in multiple numbers divided by theorientation control windows93 but connected into one at a region not shown.

InFIG. 16, the region just below theorientation control slope91 is a boundary in the orientation direction of the liquid crystal and forms a light-shielding region. And, thedrain signal line80 is disposed there to overlap with the light-shielding region, so that the aperture ratio can be improved. Theorientation control window93 on thepixel electrode19 is also a boundary in the orientation direction to form the light-shielding region. By disposing thedrain signal line80 there, the distance between theorientation control window93 and thedrain signal line80 becomes so close that the orientation of the liquid crystal is disturbed by the electric field produced from thedrain signal line80 different from the aforesaid first to fifth embodiments in which the liquid crystal and the like are present therebetween. Therefore, thedrain signal line80 is most preferably disposed on an area which is the boundary of the orientation and where thepixel electrode19 is formed.

The subject matter of the present invention seen from the aforesaid respective embodiments is that wiring is disposed to overlap with the boundary in the orientation direction produced by the orientation divider. Specifically, the boundary in the orientation direction is produced whatever orientation divider is adopted, and the liquid crystal is not oriented in the vicinity of the boundary. This boundary forms a region always shielding light. Therefore, the wiring is overlapped as a light-shielding region with the boundary to decrease the light-shielding area, and the aperture ratio can be improved.

It is to be understood that the sixth embodiment can adopt the delta arrangement of color pixels to perform the fourth and fifth embodiments in combination.

While there have been described that what are at present considered to be preferred embodiments of the invention, it is to be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.

Claims (6)

1. A liquid crystal display device, characterized in that:

liquid crystal is sealed between a first substrate and a second substrate which are disposed so as to oppose each other;

the first substrate has switching elements connected to gate signal lines and drain signal lines, pixel electrodes which are connected to the switching elements and made of a conductive material and a vertical orientation film for orienting the liquid crystal;

the second substrate has an opposing electrode which has orientation control windows at positions overlapping with the pixel electrodes to control the orientation of the liquid crystal and a vertical orientation film for orienting the liquid crystal;

the drain signal lines are disposed on the first substrate at positions that overlap with the orientation control window; and

the orientation control windows include a region which extends in a predetermined direction and the drain signal lines are disposed to overlap the extension region along the longitudinal direction of the extension region.

2. A liquid crystal display device according toclaim 1, wherein

the orientation control window divides the orientation direction of the liquid crystal by generating an electric field which is inclined with respect to the normal line of the pixel electrode and/ or the opposing electrode.

3. A liquid crystal display device according toclaim 1, wherein

the liquid crystal has a negative anisotropy of dielectric constant, and the vertical orientation film is formed to cover the pixel electrode.

4. A liquid crystal display device according toclaim 1, wherein

the orientation control window includes a region which overlaps the gate signal line.

5. A liquid crystal display device according toclaim 1, wherein

storage capacitors are disposed so as to correspond to the pixel electrodes,

storage capacitor lines constituting the storage capacitors are disposed on the side of the first substrate, and

the orientation control window includes a region which overlaps the storage capacitor lines.

6. A liquid crystal display device according toclaim 1, wherein

the vertical orientation film is rubbingless.

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